18 Keysight 34921A-34925A User’s Guide
Measurement Functions for the Multiplexer Modules
The MUX modules support the DMM measurement functions shown in the 
following table.
[a] Direct current measurements are allowed on channels 41 through 44 only (for all other channels, external shunts are required). 
[b] Optional 34921T Terminal Block is required for thermocouple measurements with built-in internal reference junction.
[c] A fixed or external reference junction temperature is required for thermocouple measurement with this module.
[d] Impact of higher offset voltage specification (< 50 V) must be taken into consideration.
[e] 1 k or higher range used unless 100 series resistors are bypassed on module.
[f] 10 k or higher range used for loads over approximately 300 due to series resistance of FET channels.
Measurement Function(s)
34921A
40-ch
Armature
Mux
34922A
70-ch
Armature
Mux
34923A
40-ch 
Reed Mux
(2-Wire)
34923A
80-ch  
Reed Mux
(1-Wire)
34924A
70-ch 
Reed Mux)
34925A
40-ch 
FETMux
(2-Wire)
34925A
80-ch 
FETMux
(1-Wire)
Voltage, AC/DC Yes Yes Yes Yes Yes Yes Yes
Current, AC/DC
Yes
a
No No No No No No
Frequency/Period Yes Yes Yes Yes Yes Yes Yes
Ohms 2-Wire  Yes Yes
Yes
e
Yes
e
Yes
e
Yes
f
Yes
f
Ohms 4-Wire  Yes Yes
Yes
e
No
Yes
e
Yes
f
No
Thermocouple 
Yes
b
Yes
c
Yes
c,d
Yes
c,d
Yes
c,d
Yes
c
Yes
c
RTD 2-Wire Yes Yes
Yes
e
Yes
e
Yes
e
No No
RTD 4-Wire Yes Yes
Yes
e
No
Yes
e
Yes
f
No
Thermistor  Yes Yes
Yes
e
Yes
e
Yes
e
No No